An invasive pond fern has taken over the Prospect Park lake, and nature lovers fear the verdant gunk will choke out aquatic life and make turtles blind.

A rapidly growing species called azolla caroliniana has formed a sprawling greenish sheen on surface of the lake by the boathouse in the past few weeks — potentially hogging oxygen and blocking sunlight, according to Cornell University’s Chuck O’Neill.

“It has a tendency to crowd out other plants and cause mortality in fish,” said O’Neill, who specializes in the study of invasive species. “It’s a nuisance.”

The researcher says contaminated fishing or boating equipment could have also triggered the bloom, which first made waves last year but returned this summer in greater volume.

That worries park watchdogs, who have long claimed the gunk scares away waterfowl, blinds turtles, and sickens mammals.

“It’s a serious problem; it can kill aquatic wildlife in the watercourse,” said park advocate Ed Bahlman.

A warm spring season likely triggered excessive amounts of the fern, which has spread rapidly in the past three months and is “relatively new” to Prospect Park altogether, according to taxonomists with the Brooklyn Botanic Garden and the New York Botanical Garden who tested the water after the stuff coated the lake last fall and determined it was “azolla bloom.”

Dubbed water velvet and mosquito plant, the new strand aquatic life is the “Jekyll & Hyde” of water weeds — serving as a crop-boosting miracle plant as well as an oxygen-sucking ecosystem invader, according to some experts.

A Prospect Park Alliance spokesman, Paul Nelson, sent The Brooklyn Paper a link to the agency’s website stating that the green and red gunk is not toxic and that scientists will continue to monitor it.

“We expect and hope that, being a native species, [it] will not have harmful consequences for our ecosystem,” the website notes. “That being said, we are watching closely.”

Authorities in Great Britain and China have worked to eradicate the same strand of water weed, saying it kills native wildlife and floods waterways.

When you enter Prospect Park you are expected to suspend good common sense and follow blindly along with the Alliance's misleading statements. Prospect Park has plenty of examples of "harmful consequences" that have been characterized otherwise.

July 11, 2012, 7:20 am

Miguel Carraway from Clinton Hill says:

That lake is an abomination.

July 11, 2012, 8:25 am

Pond Fern from bk says:

who da —— now Prospect Park? who da —— now!?

July 11, 2012, 8:51 am

Rob from Kensington says:

Someone should inform Paul Nelson that the Prospect Park Alliance does not own Prospect Park and he has a responsibility to treat people who go to the park with respect. It would be a good start if he stopped spewing self-serving hogwash.

July 11, 2012, 9:26 am

Roger from Windsor Terrace says:

The Alliance has an us against them mentality. Instead of working for the benefit of the park and we who use it, they come across like we are the nuisance.

July 11, 2012, 12:09 pm

Janet from Parkside Ave says:

Contaminated fishing may have contributed? Well I wish the heck they would ban fishing. Why do they allow it anyway? Awful to the fish and the threat with the line and hooks irks me.

They should ban fishing and ban barbecuing, then perhaps I would visit again.

July 11, 2012, 2:48 pm

ty from pps says:

Janet -- You don't go to Prospect Park anymore?

"then perhaps I would visit again" -- sounds a bit like either hyperbole or you wouldn't visit anyway regardless of any changes.

July 11, 2012, 3:40 pm

Joan from Windsor Terrace says:

This looks like a poorly maintained ballfield with a bridge over it. You would think the Prospect Park Alliance spokesperson would call this harmful "for our ecosytem"

July 12, 2012, 6:36 am

Russell from Prospect Heights says:

The Prospect Park Alliance has such low standards for what is acceptable and here we have another illustration of how little they care.

July 12, 2012, 7:17 am

John from Park Slope says:

Superficial supervision of the park is the Alliance's specialty, and it is nothing to be proud of. Hang your collective heads in shame.

July 12, 2012, 9:48 am

carolina from park slope says:

I went to the park this morning with my kids. The lake looks in terrible shape. The fern is everywhere. I'm afraid to let them go near it now. Something has to be done here!

July 12, 2012, 10:40 am

Kelly from Windsor Terrace says:

Prospect Park is Brooklyn's A Little Shop of Horrors without the musical comedy. Feed me Seymour (Git It)The deficiencies of the Alliance are bad enough. Each time there is a response from Nelson it is littered with ignorant smugness.

July 12, 2012, 11:03 am

Sean from Park Slope says:

The Prospect Park Alliance's credibility is as murky as the waterways. The outbreak of Azolla is a mirage. Take a drink of water, not from the lake and it will all go away.

July 12, 2012, 1:07 pm

Joe from from Schmoe says:

Ed Bahlman, where've you been?

How's Ann-katrinka?

July 12, 2012, 2:37 pm

Carol from Park Slope says:

I hope the Prospect Park Alliance is not counting on Nature's Helpers to clean up this mess.

You won't get my kids to do your work as long as you continue to let the lake fall apart.http://www.prospectpark.org/calendar/event/1522559

"Spend time outside enjoying nature while helping to keep the Park clean. Families can take a tour of the Park and its waterways and help keep it clean along the way. Gloves, garbage bags and trash grabbers will be provided."

July 12, 2012, 3 pm

Scott from Park Slope says:

This is a native species, not an industrial pollutant. Nobody did anything wrong to make this grow here. It found a niche it likes and it's growing. That's nature. Clearing it out somehow would be the un-natural thing to do, by that definition.

Now, the park is not nature in its primeval state. It's a park. So it's fine for us humans to modify the natural state in it to suit our needs and aesthetics. According to Wikipedia (http://en.wikipedia.org/wiki/Azolla_caroliniana) this plant has uses in agriculture and as feedstock for fish. Azolla fixes nitrogen from the atmosphere, apparently, so it's useful as a fertilizer. Why couldn't the Park harvest it and use it to fertilize plantings around the place?

July 13, 2012, 10:14 am

Scott from Park Slope says:

Also, it seems fish like koi and tilapia like to eat Azolla (http://onestrawrob.com/?p=1868). The Brooklyn Botanic Garden has fine specimens of koi in their Japanese Garden pond. Perhaps they'll lend Prospect Park a few. Alternatively, the Park could introduce tilapia to the lake and make the recreational fishermen happy.

Anyway it seems there's an opportunity to kill several birds with one stone here.

July 13, 2012, 10:21 am

Carl from Park Slope says:

Clueless Scott is at again with another quick fix. No need for him to visit the site, presto-chango he has a solution. Just what the waterways need, tilapia taking over where the Azolla leaves off.You could work for the Alliance -

"Because tilapiine cichlids are generally large, fast growing, breed rapidly, and tolerate a wide variety of water conditions (even marine conditions), once introduced into a habitat they generally establish themselves very quickly. In doing so they compete with native fish fauna, create turbidity in the water (by digging) thus reducing the light available for aquatic plants, and eating certain types of aquatic plants causing changes in local aquatic flora."

July 13, 2012, 11:22 am

Scott from Park Slope says:

I visit the site all the time. I run by it every day. I take my kids to play in the Audubon Center. The duckweed (the Azolla in question) dies out over the winter; in early spring it isn't present; by middle to late summer it's a thick carpet. Duckweed isn't an invasive species like the fragmite the Park has been battling for years. It's native. It naturally grows in habitats like the Lullwater in Prospect Park.

The Lake and Lullwater, however, are themselves artificial (http://en.wikipedia.org/wiki/Prospect_Park_%28Brooklyn%29: "All the waterways and lakes in Prospect Park are man-made."). So any "native fish fauna" in the watercourse were placed there. We humans can therefore choose to place other species there that better suit the needs of the Park without disrupting any "natural" habitat.

If people who use the park don't like the duckweed that builds up in the Lullwater, then there are a couple things that can be done that are more useful than complaining. One is to use the duckweed as fertiliser the same as is done in Asia. The other is to introduce fish species that will keep the duckweed in check and provide enjoyment to human visitors in other ways including aesthetics and sport.

If you hate the catching & eating of fish, if you hate the idea of food coming from any place that isn't Key Foods or C-town, if you despise fishermen, hikers, hunters, and outdoorsmen of all stripes, then by all means don't introduce tilapia. Koi are nice, too. The pond in the Japanese Garden in the BBG is the right habitat for duckweed, too, but it has koi and seems to do OK. Perhaps the folks who manage that resource for the BBG can help the Park figure out if it would work on the other side of Flatbush too.

July 16, 2012, 11:53 am

John from Park Slope says:

Scott, read the article! It's not about duckweed.You are not helping the discussion by showing an arrogance and ignorance like no other.

If only you knew what you were writing about. Stop before you expose yourself even more.

July 16, 2012, 12:58 pm

Scott from Park Slope says:

It's about azolla caroliniana, which is the same genus as duckweed fern (http://en.wikipedia.org/wiki/Azolla). It's eaten by the same fish. It's used as fertiliser because of its ability to fix nitrogen. Apparently it also suppresses mosquitos. But, hey, let's not let a little research or a quick google get in the way of a knee-jerk response.

Or perhaps some folks prefer a massive, out-of-scale response to a little water plant bloom like dumping thousands of gallons of herbicide into the water features of the park or draining all the Ravine, Lullwater, and Lake so people in hazmat suits can get out there and polish the watershed clean one millimeter at a time. You can do that, but then you can't also continue to claim to be an environmentalist or concerned about the park or anything of the kind.

Because you really are talking about doing something immensely foolish like that, or simply talking to the guys. right. next. door. at BBG who deal with the same issues and keep them successfully in check.

July 16, 2012, 5:27 pm

Chris from Windsor Terrace says:

Gee Scott, you can't be stopped can you from spilling your useless dribble wherever you troll.

Googling your brains out and misinterpreting articles is a sad and lonely way to spend time and qualifies you as a big zero.

July 16, 2012, 5:50 pm

Scott from Park Slope says:

Chris, wonderful rejoinder. I do enjoy insightful posts like yours. Can you be bothered to learn anything about ecology, or park management, or history, or common library skills? It's unreasonable to ask you, a city slicker, to appreciate the outdoorsman's perspective. It's unreasonable to ask you, an alarmist and Sierra-Club stooge, to understand the difference between pristine wilderness and managed spaces. It's also, apparently, to learn the difference between a learned person who disagrees with you on a particular issue and what it means to call someone, online, a 'troll.'

But, hey, let's throw our hands up in the air, run around like Chicken Little, and throw stones at the good people who run our parks. That's a much better solution than thinking.

July 29, 2012, 4:53 pm

concerned from PPS says:

The water quality is disgusting. It amazes me that people let their dogs swim there! Dog Beach should be closed down...and where is FIDO? Isn't safety of dogs in the park kind of their area?

Oct. 10, 2012, 9:10 am

Albert from Framingham, MA says:

Lighten up people. Prospect Park is a marvelous asset. Azolla will not harm wildlife. It will improve water quality, and perhaps if you comtemplate it , it will make several of you more civil. Blind turtles indeed!Talk to the people next door at theGarden

Dec. 25, 2013, 5:01 pm

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